1. Field of the Invention
This invention pertains to sorting machines that optically sort or separate substandard fungible items from standard items as the items flow past a viewing window of such a machine and in front of a standardized background.
2. Description of the Prior Art
A typical sorting machine of the type with which the present invention is used is a high speed sorting machine typically used for sorting fungible products in the food industry or otherwise. For example, individual coffee beans are caused to flow by gravity feed down a steep channel or chute to be sorted by such a machine to separate "substandard" beans from standard ones. The term "substandard" applies to beans that are outside of a predetermined acceptable range of "color" hue in one or more bands of radiation, which bands are in some cases outside of the visible color spectrum. In the simplest case, the items are sorted for variation from a hue or shade of color, including a shade of black or white and thus a shade of gray, in a single spectrum. Such a sorting procedure is referred to as monochromatic sorting since only a single radiation spectrum is being observed. In a more complex optical color sorting operation, the flow of items is sorted to determine when an item is reflecting an unacceptable radiation amount in either of two radiation bands. Such a sorting procedure is referred to as bichromatic sorting. It will be apparent that more than two radiation bands can be employed, if desired.
Optical sorting machines of the type generally described above employ optical sensors that include one or more photodetectors, such as photodiodes. The photodetectors are positioned to observe the illuminated product stream through a light admitting window. The stream passes between an optical sensor and a background having a color or shade that matches the product stream in standard color or shade so that only a variation in a product color or shade causes a detection event. The illumination is from one or more lamps directed at the product stream to cause standard reflectivity from standard products in the one or more radiation bands being observed and to cause substandard reflectivity from substandard products in those bands.
The machines also include an ejector mechanism located downstream from the sensor or sensors and actuated by an electrical signal originating from sensor detection. When a substandard item or product is detected, an electrical signal is produced and the ejector is actuated just as the substandard product and the mechanism are in alignment. Therefore, there is a very slight delay from the time of sensing to the time of ejecting. The typical ejector mechanism is usually an air ejector.
As mentioned, the product stream flows in front of a background having a color or shade that is critical to the overall operation in that it has to match the standard product under detection in the wavelength or bands being observed by the sensors. This is usually accomplished by carefully painting the background, letting the background dry and then operating the machine or otherwise analyzing whether the color or shade of the background is acceptable. For bichromatic sorting, the background has to be acceptable in reflectivity characteristics in two bands, which is not always easy to tell by a casual observation. Much time is consumed by such a procedure, and such trial-and-error technique still can result in not matching exactly the acceptable radiation ranges as desirably as could be otherwise accomplished by the invention hereafter described. Moreover, when a new selection criterion or criteria is desired, such as for a sort of a different coffee bean from the first sort, the background has to be tediously changed. This change can be by repainting the background or by changing the background to one having the new color or shade that had previously been determined.
Even when a background color is determined in the prior art way just described, a run of a stream of products can cause the background color or shade to change greatly. This is because of paint fading over a period of time, the accumulation of product dust, or the like.
The need for having a dynamically variable background for a sorting machine was recognized and a procedure is disclosed therefor in U.S. Pat. No. 4,863,041, Roger F. Bailey, which patent issued Sep. 5, 1989. The Bailey patent utilizes a plurality of photosensors viewing respectively separate background assemblies. Each background assembly is the end of a bundle of fiber optic fibers. The light into the fibers is controlled typically by two light sources, one source at each of two spectral wavelengths obtained by the use of an appropriate dichroic mirror. Adjustment of the mix of the two light sources is achieved by adjusting the respective voltages on the two sources. Although fiber optic cables are predictable and useful for transmitting light in the visible spectrum, sorting using spectrum ranges in the infrared spectrum is not compatible with fiber optics since such signals fade with fiber optics of varying lengths in a manner that is often unpredictable and not readily controllable. Adjustment to different spectral ranges using the same fiber optics results in fading to different degrees than for the previous ranges, making fiber optics totally unsuited for background determination in such sorting machines.
Therefore, it is a feature of the present invention to provide an improved variable background for sorting machines to allow spectral adjustment in at least one and preferably in two or more spectral ranges, including the infrared ranges.
It is another feature of the present invention to provide an improved variable background for sorting machines employing a frosted glass or the like and one or more adjustable light sources for changing the reflectivity of the background in one or more spectral ranges.
It is still another feature of the present invention to provide an improved variable background for sorting machines including a frosted glass or the like, a beamsplitter and two light sources for changing the reflectivity of the background in two separated spectral ranges.